Purple soft cap is level 9, its not worth leveling to 10.

Orange, i have gone up to level 8 so far.

Red, i have gone up to level 6 so far.

Mainly, think about how efficient it is to spend the coins leveling up each rune.

If you have a red and purple level 5. the cost of leveling red will be the same as leveling purple to 8 or 9.

So you need to weigh how much additional stats u are getting from both and which is better value.